Ambient energy harvesting systems are used in various applications to provide power without reliance on a power grid. Radio frequency (RF) energy sources are attractive because of RF's relative ubiquity and intrinsic ability to penetrate opaque walls, making it generally available at all times. However, typical ambient RF energy harvesters cannot generate output voltage that is high enough to power many circuits (such as integrated circuits (ICs)). This limits the use of RF energy harvesters in the related art to places having a strong RF energy source. Meanwhile, solar energy harvesting devices (e.g., photovoltaic (PV) cells) can provide high power when exposed to sunlight, but the power from a PV cell decreases at least linearly with decreases in light intensity. That is, the energy conversion efficiency of PV cells is limited with limited lighting by increased power losses that arise as the value of the devices shunt resistance becomes comparable to the characteristic resistance of the cell. Thus, solar energy harvesting devices can only provide intermittent power.
In the related art, hybrid energy harvesting systems utilizing multiple energy sources, for example solar and heat, have been used to improve the conversion efficiency and increase the available power over a single energy harvesting system. However, such related-art hybrid energy harvesting systems are not well-suited for low-power, but long-life applications, such as, for example, internet of things (IoTs) devices. For example, certain related art approaches utilizing both RF energy harvesters and solar energy harvesters fail to improve over the use of a solar energy harvest because most of the power is provided by solar cells. Thus, these types of devices traditionally heavily rely on a primary battery, which must be replaced. However, battery replacement can be time-consuming, labor intensive, and inefficient. Accordingly, there is needed a power source which can autonomously maintain the operation of these devices with ambient energy without heavy reliance on a battery.
Aspects of the present disclosure address these and other issues. Certain implementations consistent with the present disclosure utilize a unique and nonobvious configuration of converting power provided by a higher-density, low voltage power source into a higher-voltage, usable energy form, and controlling the converter with a higher-voltage but lower density energy source. Moreover, in some cases, the energy harvesters, converters, and fundamental circuit components may be formed using inkjet printing technology to provide exceptionally thing form-factor.